Prioritize @Serializable annotation on type usage over class usage

In `val p: @Serializable(X) Foo` and `@Serializable(Y) class Foo` situation,
now X would be chosen as serializer.

Fixes https://github.com/Kotlin/kotlinx.serialization/issues/1895

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerSearchUtil.kt

@@ -46,7 +46,7 @@ fun BaseIrGenerator.getIrSerialTypeInfo(property: IrSerializableProperty, ctx: S
     val T = property.type
     property.serializableWith(ctx)?.let { return SerializableInfo(it) }
     findAddOnSerializer(T, ctx)?.let { return SerializableInfo(it) }
-    T.overridenSerializer?.let { return SerializableInfo(it) }
+    T.overriddenSerializer?.let { return SerializableInfo(it) }
     return when {
         T.isTypeParameter() -> IrSerialTypeInfo(property, if (property.type.isMarkedNullable()) "Nullable" else "", null)
         T.isPrimitiveType() -> IrSerialTypeInfo(
@@ -112,7 +112,7 @@ fun analyzeSpecialSerializers(
 
 
 fun findTypeSerializer(context: SerializationBaseContext, type: IrType): IrClassSymbol? {
-    type.overridenSerializer?.let { return it }
+    type.overriddenSerializer?.let { return it }
     if (type.isTypeParameter()) return null
     if (type.isArray()) return context.referenceClassId(referenceArraySerializerId)
     if (type.isGeneratedSerializableObject()) return context.referenceClassId(objectSerializerId)
@@ -166,8 +166,9 @@ internal fun IrClass.polymorphicSerializerIfApplicableAutomatically(context: Ser
     }
 }
 
-internal val IrType.overridenSerializer: IrClassSymbol?
+internal val IrType.overriddenSerializer: IrClassSymbol?
     get() {
+        annotations.serializableWith()?.let { return it }
         val desc = this.classOrNull ?: return null
         desc.owner.serializableWith?.let { return it }
         return null

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt

@@ -538,7 +538,7 @@ fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty, ty
 
     property.serializableWith?.toClassDescriptor?.let { return SerializableInfo(it) }
     findAddOnSerializer(property.type, property.module)?.let { return SerializableInfo(it) }
-    property.type.overridenSerializer?.toClassDescriptor?.let { return SerializableInfo(it) }
+    property.type.overriddenSerializer(property.module)?.toClassDescriptor?.let { return SerializableInfo(it) }
 
     if (property.type.isTypeParameter()) return JVMSerialTypeInfo(
         property,

plugins/kotlinx-serialization/kotlinx-serialization.k1/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/TypeUtil.kt

@@ -54,7 +54,7 @@ fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty): S
     val T = property.type
     property.serializableWith?.toClassDescriptor?.let { return SerializableInfo(it) }
     findAddOnSerializer(T, property.module)?.let { return SerializableInfo(it) }
-    T.overridenSerializer?.toClassDescriptor?.let { return SerializableInfo(it) }
+    T.overriddenSerializer(property.module)?.toClassDescriptor?.let { return SerializableInfo(it) }
     return when {
         T.isTypeParameter() -> SerialTypeInfo(property, if (property.type.isMarkedNullable) "Nullable" else "", null)
         T.isPrimitiveNumberType() or T.isBoolean() -> SerialTypeInfo(
@@ -147,7 +147,7 @@ fun AbstractSerialGenerator?.findTypeSerializerOrContext(
 }
 
 fun findTypeSerializer(module: ModuleDescriptor, kType: KotlinType): ClassDescriptor? {
-    val userOverride = kType.overridenSerializer
+    val userOverride = kType.overriddenSerializer(module)
     if (userOverride != null) return userOverride.toClassDescriptor
     if (kType.isTypeParameter()) return null
     if (KotlinBuiltIns.isArray(kType)) return module.getClassFromInternalSerializationPackage(SpecialBuiltins.referenceArraySerializer)

plugins/kotlinx-serialization/kotlinx-serialization.k1/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt

@@ -245,13 +245,13 @@ val ClassDescriptor?.classSerializer: ClassDescriptor?
 val ClassDescriptor.hasCompanionObjectAsSerializer: Boolean
     get() = isInternallySerializableObject || companionObjectDescriptor?.serializerForClass == this.defaultType
 
-// returns only user-overriden Serializer
-val KotlinType.overridenSerializer: KotlinType?
-    get() {
-        val desc = this.toClassDescriptor ?: return null
-        desc.serializableWith?.let { return it }
-        return null
-    }
+// returns only user-overridden Serializer
+fun KotlinType.overriddenSerializer(module: ModuleDescriptor): KotlinType? {
+    annotations.serializableWith(module)?.let { return it }
+    val desc = this.toClassDescriptor ?: return null
+    desc.serializableWith?.let { return it }
+    return null
+}
 
 val KotlinType.genericIndex: Int?
     get() = (this.constructor.declarationDescriptor as? TypeParameterDescriptor)?.index

plugins/kotlinx-serialization/testData/boxIr/serializableOnPropertyType.kt

@@ -0,0 +1,56 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import kotlinx.serialization.internal.*
+
+
+@Serializable(BruhSerializerA::class)
+class Bruh(val s: String)
+
+object BruhSerializerA : KSerializer<Bruh> {
+    override val descriptor: SerialDescriptor
+        get() = PrimitiveSerialDescriptor("Bruh", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: Bruh) {
+        encoder.encodeString(value.s)
+    }
+
+    override fun deserialize(decoder: Decoder): Bruh {
+        return Bruh(decoder.decodeString())
+    }
+}
+
+object BruhSerializerB : KSerializer<Bruh> {
+    override val descriptor: SerialDescriptor
+        get() = PrimitiveSerialDescriptor("Bruh", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: Bruh) {
+        encoder.encodeString(value.s + "#")
+    }
+
+    override fun deserialize(decoder: Decoder): Bruh {
+        return Bruh(decoder.decodeString().removeSuffix("#"))
+    }
+}
+
+typealias BruhAlias = @Serializable(BruhSerializerB::class) Bruh
+
+@Serializable
+class Tester(
+    val b1: Bruh,
+    @Serializable(BruhSerializerB::class) val b2: Bruh,
+    val b3: @Serializable(BruhSerializerB::class) Bruh,
+    val b4: BruhAlias
+)
+
+fun box(): String {
+    val t = Tester(Bruh("a"), Bruh("b"), Bruh("c"), Bruh("d"))
+    val s = Json.encodeToString(t)
+    if (s != """{"b1":"a","b2":"b#","b3":"c#","b4":"d#"}""") return s
+    return "OK"
+}

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java

@@ -105,6 +105,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
             runTest("plugins/kotlinx-serialization/testData/boxIr/sealedInterfaces.kt");
         }
 
+        @Test
+        @TestMetadata("serializableOnPropertyType.kt")
+        public void testSerializableOnPropertyType() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/serializableOnPropertyType.kt");
+        }
+
         @Test
         @TestMetadata("starProjections.kt")
         public void testStarProjections() throws Exception {

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java

@@ -103,6 +103,12 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
         runTest("plugins/kotlinx-serialization/testData/boxIr/sealedInterfaces.kt");
     }
 
+    @Test
+    @TestMetadata("serializableOnPropertyType.kt")
+    public void testSerializableOnPropertyType() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/serializableOnPropertyType.kt");
+    }
+
     @Test
     @TestMetadata("starProjections.kt")
     public void testStarProjections() throws Exception {